The present invention relates to centrifugal pumps in general, and more particularly to improvements in centrifugal pumps having volute casings. Still more particularly, the invention relates to improvements in centrifugal pumps with double volute casings.
The casing or housing of a pump serves to seal the conveyed fluid from the surrounding area. This can be achieved independently of the exact shape of the casing. However, and in order to be capable of carrying out certain specific tasks, the casings of centrifugal pumps normally assume one of a large number of different shapes which enable them to perform given functions more satisfactorily than centrifugal pumps having casings of a different configuration. Double volute casings are one of a large category of pump casings which can be used in centrifugal pumps, and their function is to balance the radial thrust. The two volutes are disposed opposite and are normally similar to one another. As a rule, the starts of the two volutes are offset 180 degrees in relation to each other. Such design is believed to ensure that the radial thrust is not only constant but also that the radial thrust is small or negligible within the entire operating range of the centrifugal pump. Depending on the structural design of the centrifugal pump, the volutes surround the impeller which is rotatably mounted in the casing, or they surround a guide wheel or diffuser which is installed in the pump casing downstream of the impeller.
German Offenlegungsschrift No. 26 40 866 discloses a centrifugal pump whose casing has two volutes which are offset relative to one another. The first volute extends beyond the start of the second volute and the casing has channels which connect the end of the first volute with the outlet nozzle. The latter is common to both volutes. A drawback of such centrifugal pumps is that the casing is relatively large owing to the dimensions of the volutes, as considered radially of the casing. This entails greater pressures and results in greatly increased bulk of the casing, especially when compared with a single volute casing.